This invention relates to communication systems, including but not limited to calls involving peripheral devices in communication systems.
Communication systems are known to comprise an infrastructure, typically including a plurality of base stations, a controller, a home location register (HLR), and a mobile switching center (MSC), that provides communication services to communication units located in corresponding service coverage areas of the base stations. One example of such a communication system is a cellular communication system. In a cellular system, a remote unit (e.g., a mobile or portable radiotelephone) that desires to communicate, sends a channel request message to a base station serving the coverage area in which the remote unit is located. Upon receiving the channel request message, the infrastructure of the cellular system allocates a communication channel for the communication, and the remote unit begins communicating with a telephone network subscriber or another remote unit via the serving base station. Typically, multiple access wireless communication between the base station and the remote stations occurs via radio frequency (RF) channels that provide paths over which communication signals such as voice, data, and video are transmitted.
In order to provide desirable features for a call, such as pre-paid cellular service, menu-driven information extraction, selective call acceptance, voice recognition, and wiretap to name a few, a peripheral device may be added to a communication system. Calls to or from a remote unit may be diverted to the peripheral device that performs its function and then redirects the call back to the MSC so that the call may proceed. Control of routing for calls involving a peripheral device is typically performed by an HLR via originating and terminating triggers detected by the MSC. When a trigger is detected, the MSC informs the HLR, typically by invoking an ANSI-41 standard operation. The HLR determines from the remote unit""s service profile that a peripheral service should be invoked and returns to the MSC routing instructions for the peripheral device.
ANSI-41 defines the operations that are used for trigger detection and HLR involvement in call routing decisions as single TCAP (Transaction Capability Application Part) transaction, i.e., transactions occur without recording a history. TCAP is a transaction-oriented protocol defined for use with Signaling System No. 7, as is known in the art. For a call that needs to be routed to only a single peripheral device, a single TCAP transaction will suffice. When transactions with one or more peripheral devices must be provided for a call, the single TCAP transaction operations used by the HLR present a problem because the HLR has no way of knowing which peripheral device, if any, has already been invoked or which peripheral device should be invoked next. If present ANSI-41 operations were to be used to invoke one or more different peripheral devices, the call would likely end up in an endless loop trying to access the first peripheral device involved in the call.
Accordingly, there is a need for a method of routing a call to one or more peripheral devices prior to call completion.